Battery module gas sensor for battery cell monitoring

ABSTRACT

Battery monitoring systems and methods are provided. The battery monitoring system may include a battery module and battery management circuitry. The battery module comprises battery cells and a gas sensor configured to detect the presence of gas within the battery module. The battery management circuitry is configured to receive a sensor signal from the gas sensor, determine whether the sensor signal indicates the presence of gas within the battery module, and in response to determining that the sensor signal indicates the presence of gas, take an action. The action may include increasing cooling to the battery cells, limiting a maximum load that can be applied to the battery module, disconnecting the battery module, or providing a warning. The battery module may also include a component that was doped with a chemical that begins to off-gas above an activation temperature. The gas sensor may be configured to detect the chemical.

CROSS REFERENCE TO RELATED APPLICATION

This disclosure claims the benefit of U.S. Provisional Application No.62/808,220, filed Feb. 20, 2019, which is hereby incorporated byreference herein in its entirety.

SUMMARY

Battery modules having multiple battery cells are used in a variety ofapplications. For example, electric vehicles can use battery moduleshaving a large number of battery cells (e.g., hundreds or thousands ofbattery cells per module). It is important that battery modules are notoperated outside of their safe operating regions. When a battery cell,such as a lithium ion battery cell, is operated above its safe operatingtemperature, damage can occur. As the temperature rises, pressure canbuild up in the battery cell. For example, electrolyte gel inside of thebattery cell can begin to bubble or generate steam, which causes thepressure inside of the battery cell to increase. Battery cells typicallyhave a vent that allows gas or liquid to escape when pressure increasesbeyond the actuation pressure of the vent. It is desirable to preventbattery cells from reaching ventilation. In addition, if the temperatureinside of a battery cell continues to increase, a thermal runaway eventcan occur. It is also desirable to prevent a thermal runaway event.

Battery management systems are used to monitor the operation of batterymodules to ensure that they are operated within a safe operating region.One way of monitoring the temperature of a battery cell is to use atemperature sensor such as a thermistor or thermocouple. When a batterymodule contains multiple battery cells, multiple temperature sensor maybe needed to sufficiently monitor the temperature of the battery cells.In some systems, the thermal properties of a battery module are modeledand the model can be used to reduce the number of temperature sensors.However, such systems may not be able to detect a localized temperatureincrease in time to prevent damage to one or more battery cells.Accordingly, it is desirable to identify a localized increase intemperature inside of a battery module. It is also desirable to identifya localized increase in temperature without using a temperature sensorfor each battery cell. It is also desirable to predict and prevent apotential battery cell ventilation. It is also desirable to detect theoccurrence of a battery cell ventilation. It is also desirable topredict and prevent a thermal runaway event. In accordance with someembodiments of the present disclosure, one or more gas sensors are usedin a battery module to provide improved monitoring of the batterymodule.

In some embodiment, the battery monitoring system of the presentdisclosure may include a battery module and battery managementcircuitry. The battery module comprises a plurality of battery cells anda gas sensor configured to detect the presence of gas within the batterymodule. The battery management circuitry is configured to receive asensor signal from the gas sensor, determine whether the sensor signalindicates the presence of gas within the battery module, and in responseto determining that the sensor signal indicates the presence of gas,take an action.

In some embodiments, the action comprises using a battery cooling systemto provide increased cooling to the plurality of battery cells. In someembodiments, the action comprises limiting a maximum load that can beapplied to the battery module. In some embodiments, the action comprisesdisconnecting the battery module from a load. In some embodiments, theaction comprises using a user interface to provide a warning.

In some embodiments, the battery module comprises a component that wasdoped with a chemical. When the temperature of the component increasesabove an activation temperature, the component begins to off-gas thechemical. In some embodiments, the gas sensor is configured to detectthe chemical. In some embodiments, the component comprises an adhesiveused to secure the plurality of battery cells in the battery module.

In some embodiments, the battery module comprises a first and second gassensor, where the first gas sensor is configured to detect at least onechemical that is indicative of overheating of a battery cell and thesecond gas sensor is configured to detect at least one chemical that isindicative of battery cell ventilation.

In some embodiments, the battery module comprises a first and second gassensor, where the first gas sensor is configured to detect at least onechemical that is indicative of battery cell ventilation and the secondgas sensor is configured to detect at least one chemical that isindicative of a battery cell thermal runaway event.

In some embodiments, the battery management circuitry is configured todetermine whether the sensor signal indicates the presence of gas withinthe battery module by determining whether the sensor signal indicatesthat a concentration of gas is greater than a threshold.

In some embodiments, the battery management circuitry is configured todetermine a first battery module condition when the sensor signalindicates that a concentration of gas is greater than a first thresholdand determine a second battery module condition when the sensor signalindicates that a concentration of gas is greater than a second thresholdgreater than the first threshold.

In some embodiments, the system further comprises a temperature sensorand the battery management circuitry is configured to receive atemperature sensor signal from the temperature sensor and determine abattery module condition based on the sensor signal and the temperaturesensor signal.

In some embodiment of the present disclosure, a battery monitoringmethod is provided. The method includes receiving a sensor signal from agas sensor configured to detect the presence of gas within a batterymodule, where the battery module comprises a plurality of battery cells.The method further includes determining, using battery managementcircuitry, whether the sensor signal indicates the presence of gaswithin the battery module and in response to determining that the sensorsignal indicates the presence of gas, taking an action. In someembodiments, the action comprises the actions discussed above.

In some embodiments, the method further includes doping a component ofthe battery module with a chemical, wherein when the temperature of thecomponent increases above an activation temperature, the componentbegins to off-gas the chemical. The method further includes detectingthe chemical using the gas sensor. In some embodiments, the componentcomprises an adhesive and the method further includes using the adhesiveto secure the plurality of battery cells in the battery module.

In some embodiments, the method comprises receiving first and secondsensor signals from first and second gas sensors. In some embodiments,the first gas sensor is configured to detect at least one chemical thatis indicative of overheating of a battery cell and the second gas sensoris configured to detect at least one chemical that is indicative ofbattery cell ventilation. In some embodiments, the first gas sensor isconfigured to detect at least one chemical that is indicative of batterycell ventilation and the second gas sensor is configured to detect atleast one chemical that is indicative of a battery cell thermal runawayevent.

In some embodiments, the determining whether the sensor signal indicatesthe presence of gas within the battery module comprises determiningwhether the sensor signal indicates that a concentration of gas isgreater than a threshold.

In some embodiments, determining whether the sensor signal indicates thepresence of gas within the battery module comprises determining a firstbattery module condition when the sensor signal indicates that aconcentration of gas is greater than a first threshold and determining asecond battery module condition when the sensor signal indicates that aconcentration of gas is greater than a second threshold greater than thefirst threshold. In some embodiments, taking the action comprises takinga first action in response to determining the first battery modulecondition and taking a second action in response to determining thesecond battery module condition.

In some embodiments, the method further includes receiving a temperaturesensor signal from a temperature sensor and determining a battery modulecondition based on the sensor signal and the temperature sensor signal.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure, in accordance with one or more variousembodiments, is described in detail with reference to the followingfigures. The drawings are provided for purposes of illustration only andmerely depict typical or example embodiments. These drawings areprovided to facilitate an understanding of the concepts disclosed hereinand shall not be considered limiting of the breadth, scope, orapplicability of these concepts. It should be noted that for clarity andease of illustration these drawings are not necessarily made to scale.

FIG. 1 shows an illustrative plot of gas concentration in a batterymodule in accordance with some embodiments of the present disclosure;

FIG. 2 shows a block diagram of an illustrative battery module 200 inaccordance with some embodiments of the present disclosure;

FIG. 3 shows illustrative plots of gas concentration and temperature ina battery module in accordance with some embodiments of the presentdisclosure;

FIG. 4 shows an illustrative plot of gas concentration in a batterymodule and an adjustable threshold in accordance with some embodimentsof the present disclosure; and

FIG. 5 shows a system diagram of an illustrative battery system 100 foruse in an electric vehicle in accordance with some embodiments of thepresent disclosure.

DETAILED DESCRIPTION

In accordance with the present disclosure, a gas sensor is provided in abattery module to determine the battery module status. In someembodiments, the gas sensor is used to determine the temperature of thebattery cells. In some embodiments, the gas sensor is used to predict abattery cell ventilation event. In some embodiments, the gas sensor isused to detect the occurrence of a battery cell ventilation. In someembodiments, the gas sensor is used to predict the occurrence of athermal runaway. In some embodiments, the gas sensor is used to detectthe occurrence of a thermal event.

A battery cell ventilation is a dangerous event, which can potentiallylead to explosions and fire, which can then propagate to other nearbybattery cells. In electric vehicle design, it is important to preventbattery cell ventilation by mechanical design and software controls. Ifthese mechanisms are not sufficient, it is useful to detect aventilation event in order to, for example, warn the driver and safelyshut down vehicle power.

Tests were performed to analyze the conditions inside of a batterymodule when a battery cell was purposefully overheated to induce cellventilation. The overheating of a battery cell was accomplished using anichrome wire. Gas sensors were included inside of the battery moduleenclose. A review of the test data showed, for example, a steadyincrease in detected gas concentration up to 20 minutes before theheated battery cell actually vented. Lithium-ion battery cells vent ataround 130 degrees C. As the test progressed, the cell was heated fromambient up to 130 degrees C., and the gas concentration noticeablyincreased between 100 degrees C. and 130 degrees C.

It is believed that either the battery cell was releasing a gas prior tofull ventilation or that something in thermal contact with the batterycell was releasing a gas. Gas can be released, for example, when amaterial melts or when a material is heated up and begins to off-gas.

FIG. 1 shows an illustrative plot 100 of gas concentration in a batterymodule in accordance with some embodiments of the present disclosure.Plot 100 is a simplified plot showing gas concentration as thetemperature of a battery cell increases. Plot 100 is divided into fourtemperature regions as illustrated. The first temperature region is thesafe operating region. In this region, the temperature of the batterycell is in its normal operating region. As shown, the gas concentrationis negligible. The second temperature region is the cell overheatingregion. In this region, the temperature of the battery cell is higherthan its normal operating temperature. At the low end of the celloverheating region, the gas concentration may still be negligible. Asthe battery cell temperature increases in the cell overheating region,the gas concentration starts to increase at a relatively low rate untilthe temperature reaches the cell ventilation region. In the cellventilation region, the pressure inside of the battery cell exceeds theactivation pressure of its vent and the battery cell begins to vent gasand/or liquid into the battery module. As shown, the gas concentrationincreases at a higher rate in the cell ventilation region. The lasttemperature region is the thermal runaway region. In this region, theoverheating of the battery cell causes damage to the internal structureof battery, which cause a short circuit. This then causes a fire andpotentially an explosion. In this region, the battery cell temperatureand the gas concentration in the battery module increase very quickly.

It will be understood that the specific temperature regions and gasconcentrations for a battery module will be determined based on thespecific battery cells used and the overall design of the batterymodule. For example, different types of batteries undergo ventilationand thermal runaway at different temperatures. As another example, theinternal volume of the battery module will affect the gas concentrationlevel. It will also be understood that battery modules can be designedachieve a desired relationship between battery cell temperature and gasconcentration. For example, in some battery modules, an adhesive is usedto secure the battery cells inside of the battery module. The adhesivemay be in direct contact with the battery cell and some adhesivesrelease volatile organic compounds (VOCs) when the adhesive is heatedabove a certain temperature. For example, an adhesive may begin tooff-gas vapor at about 100 degrees C., which is lower than the batterycell ventilation temperature. Accordingly, an adhesive can be selectedto provide advance warning of a potential battery cell ventilation. Suchan advance warning enables one or more actions to be taken to preventdamage to the battery cells.

In some embodiments, materials can be added to the battery module toobtain a desired relationship between gas concentration and battery celltemperature. For example, one or more components (e.g., an adhesive) ofthe battery module can be doped with a chemical such that when thetemperature of the component increases above an activation temperature,the component begins to off-gas the chemical such that it can bedetected with a gas sensor. As another example, a component can be addedto the battery module to begin off-gassing at a desired temperature.Such a component (e.g., a gel or adhesive) can be added to the outsideof battery cells to enable accurate identification of localizedoverheating.

In some embodiments, by detecting specific chemical signatures (e.g.,using an appropriately matched gas sensor substrate) and measuring theirconcentrations, the concentrations can be correlated to one or morespecific temperature points. Therefore, a single sensor can provide fullcoverage for all cells in a battery module. For example, a batterymodule can be modeled or designed to enable the gas concentrationmeasured by a single sensor to be correlated to one or more desiredbattery cell temperatures.

FIG. 2 shows a block diagram of an illustrative battery module 200 inaccordance with some embodiments of the present disclosure. Batterymodule 200 includes a plurality of battery cells 202 arranged in twolayers with a cooling plate 204 positioned between the layers. In someembodiments, the ends of battery cells 202 are secured to cooling plate204 via adhesive. The adhesive can provide a good physical and thermalcoupling between battery cells 202 and cooling plate 204. Cooling plate204 extends beyond the outer housing of battery module 200 on one sideand includes input and output ports. A cooling system, not shown in FIG.2, provides a supply of cooling fluid to the input port of cooling plate204 and receives a return of the cooling fluid from the output port. Theflow rate and/or temperature of the cooling fluid is controlled by thecooling system. The cooling system maintains the temperature of batterycells 202 in a normal operating temperature range during operation.

Battery module 200 also includes gas sensors 206 a and 206 b andtemperature sensors 208 a and 208 b. Gas sensors 206 a and 206 b can beany suitable gas sensors for detecting gases that are emitted when thetemperature of one or more of battery cells 202 increases beyond itsnormal temperature range. As shown, gas sensor 206 a is positioned atthe top of the battery module. In some embodiments, this position ispreferred because hot air rises and gases emitted due to overheating arealso expected to rise. This position may enable gas to be detectedquicker than other positions. As shown, gas sensor 206 b is positionedat the bottom of the battery module. In some embodiments, thepositioning of cooling plate 204 may make this position preferred in thebottom half of the battery module. While hot air rises, cooling plate204 will cool off the air at the top of the bottom half of the batterymodule and cause a convection current to occur, thereby moving emittedgas past gas sensor 206 b. Temperature sensors 208 a and 208 b can bepositioned at any suitable locations for measure temperature withinbattery module 200. While a temperature sensor may not be able toimmediately detect a localized temperature increase in a battery cell,it may detect such an increase if the localized temperature increasepersists. Therefore, the gas concentration and one or more temperaturereadings can be used together to determine the condition of the batterymodule. It will be understood that the design and layout of batterymodule 200 is merely illustrative and the sensors can be positioned atany suitable positions. In some embodiments, one or more guides can beused to direct the flow of hot gas towards the location of the gassensor or gas sensors. It will also be understood that while batterymodule 200 is shown with two layers of battery cells 202, more or lesslayers of battery cells can be used. It will also be understood thatmore or less gas and temperature sensors can be used. In someembodiments, a battery module includes a single layer of battery cellsand a single gas sensor.

FIG. 3 shows illustrative plots of gas concentration and temperature ina battery module in accordance with some embodiments of the presentdisclosure. Plot 300 is a simplified plot showing gas concentration 302over time in the battery module. Plot 310 is a simplified plot showingtemperature 312 over time in the battery module. The time axes of plots300 and 310 are aligned and correspond to the same time. Before time t₁,gas concentration 302 and temperature 312 remain at relatively constantlevels and this may correspond to the battery module operating in anormal operating region. Between time t₁ and time t2, gas concentration302 starts to increase while temperature 312 remains at its constantlevel. During this time interval, the battery module may beginexperiencing a battery cell overheat condition, but before theoverheating is reflected at the temperature sensor. At time t2,temperature 312 also starts to increase and thus both gas concentration302 and temperature 312 are increasing after time t2. This maycorrespond to the battery cell overheat condition persisting or gettingworse.

Plot 300 depicts two thresholds, lower threshold 304 a and upperthreshold 304 b. In some embodiments, when gas concentration 302 crossesupper threshold 304 a battery module condition (e.g., a battery overheatevent) may be declared. For example, upper threshold 304 may be selectedsuch that when gas concentration 302 crosses this threshold, a batterymodule condition can be declared with high confidence. In someembodiments, by using temperature 312 in combination with gasconcentration 302, a battery module condition can be detected with highconfidence sooner. For example, when the gas concentration 302 crosseslower threshold 304 a, but is below upper threshold 304 b, temperature312 can be analyzed to determine whether to declare a battery modulecondition with high confidence. In some embodiments, a change intemperature or a comparison of the temperature level to a threshold canbe used in combination with gas concentration 302. For example, abattery module condition can be declared when gas concentration 302crosses a threshold (e.g., lower threshold 304 a) and one of thefollowing conditions is met: (1) the slope of temperature 312 ispositive, (2) the slope of temperature 312 is greater than a threshold,(3) temperature 312 is greater than a threshold, or a combinationthereof.

As explained above, a gas sensor can be any suitable gas sensor fordetecting gases that are emitted when the temperature of a battery cellincreases beyond its normal temperature range. Such a gas sensor maydetect (a) off-gassing from an adhesive when a battery cell is in anoverheating condition, (b) gases that vent out of the battery cellduring ventilation, and (c) gases that are emitted during thermalrunaway. In some embodiments, multiple differently tuned gas sensors areused to detect different types of gases. A first gas sensor may be usedto detect off-gassing from an adhesive (e.g., an adhesive doped with achemical). A second gas sensor may be used to detect gases emittedduring cell ventilation and thermal runaway (e.g., CO, CO₂, and H₂). Athird gas sensor may be used to detect gases emitted during cellventilation and thermal runaway. In some embodiments, a single gassensor may be configured to separately detect different types of gas.

In some embodiments, one or more gas concentration thresholds may beused to determine a battery module condition. For example, a thresholdmay be set to identify when the battery module enters a battery celloverheating region, but before the battery cell reaches ventilation.Such a threshold may be set at a level below the bottom horizontaldashed line in FIG. 1. When the gas concentration is below thethreshold, the battery module condition is determined to be normal. Whenthe gas concentration is above the threshold, the battery modulecondition is determined to be in a battery cell overheating conditionand this predicts the onset of cell ventilation. A second higherthreshold may be used to identify when cell ventilation occurs. Forexample, such a threshold may be set at a level between the twohorizontal dashed lines in FIG. 1. When the gas concentration is abovethe second higher threshold, the battery module condition is determinedto be in cell ventilation condition and this predicts the onset of athermal runaway event. A third higher threshold may be used to identifywhen a thermal runaway event occurs. Such a threshold may be set at alevel above the higher horizontal dashed line in FIG. 1.

In some embodiments, the gas concentration in a battery module may varyduring normal operation of the battery module. For example, the gasconcentration may gradually increase the longer a battery module isoperated. As another example, the gas concentration may also increaseunder heavy loads. Accordingly, the usage and condition of the batterymodule can be monitored and the thresholds can be adjusted as a functionof usage. For example, if the gas concentration is expected to graduallyincrease during continuous operation of a battery module, the one ormore thresholds can also be gradually increased. As another example,when a battery module is not in use, the gas concentration in thebattery module is expected to decrease over time. Accordingly, the oneor more thresholds can be reduced based on the last reading of gasconcentration and how long the battery module has not been in use. Byadjusting the one or more thresholds based on the operating condition ofthe battery module, false positives can be eliminated. The expectednormal change in gas concentration can be determined by operating thebattery module under a range of normal operating conditions andobserving the changes in gas concentration.

FIG. 4 shows an illustrative plot 400 of gas concentration 402 in abattery module and an adjustable threshold 404 in accordance with someembodiments of the present disclosure. Plot 400 is simplified plotshowing gas concentration 402 over time as the battery module is under aload (e.g., a relatively constant load). As shown, threshold 404 variesover time and is therefore adjustable based on the operating conditionof the battery module. In some embodiments, battery management circuitryis used to determine the adjustable threshold. For example, theadjustable threshold can be determined by first calculating the expectedgas concentration in the battery module based on the load over time andinformation about how the battery module is expected to operate underthe load and then adding an offset (e.g., a fixed amount or a percentageamount). In FIG. 4, threshold 404 increases linearly over time under therelatively constant load. By using an adjustable threshold (e.g., basedon expected gas concentration), a battery overheat event can bepredicted or identified quickly. The gas concentration 402 in thebattery module increases linearly before time t₁ as expected. However,at time t₁ the gas concentration 402 begins to increase at a faster rateindicating that a battery overheat condition may be about to occur. Attime t2, the gas concentration 402 crosses the adjustable threshold 404.At this point, the battery management circuitry may declare a batterymodule condition (e.g., a battery overheat event) and take one or moreactions as described herein.

The battery module of the present disclosure, such as battery module 200of FIG. 2, can be used in various applications. For example, the batterymodules can be used for grid energy storage. As another example, thebattery modules can be used in an electric vehicle.

FIG. 5 shows a system diagram of an illustrative battery system 500 foruse in an electric vehicle in accordance with some embodiments of thepresent disclosure. Battery system 500 includes one or more batterymodules 502 coupled to electric vehicle subsystems 510. In someembodiments, each of the one or more battery modules 502 includesmultiple battery cells. In some embodiments, the one or more batterymodules 502 each correspond to battery module 200 of FIG. 2. Theelectric vehicle subsystems depicted in FIG. 3 are exemplary andadditional or less subsystems may be included in the electric vehicle.It will be understood that the electric vehicle subsystems may comprisecircuitry for performing functions. In some embodiments, the circuitrymay comprise hardware (e.g., one or more ASICs) or a combination ofhardware and software (e.g., one or more hardware CPUs for executingsoftware instructions stored in memory), or a combination thereof. Asshown, the electric vehicle subsystems include a battery managementsystem 512, one or more electric drive units 514, a battery coolingsystem 516, and a user interface 518.

The battery management system 512 monitors and controls the operation ofthe battery modules 502. The battery management system 512 receivessensor signals from the battery modules 502. In some embodiments, thebattery management system 512 receives sensor signals from gas sensors(e.g., gas sensor 206 a and 206 b of FIG. 2). In some embodiments, thebattery management system 512 receives sensor signals from gas sensorsand temperature sensors (e.g., temperature sensors 208 a and 208 b ofFIG. 2). The battery management system 512 (e.g., battery managementcircuitry) evaluates the sensor signals and determines the condition ofthe battery modules. When the condition of a battery module is outsideof its normal operating condition, the battery management system 512 maytake one or more actions.

The battery cooling system 516 provides cooling to the one or morebattery modules 502. In some embodiments, the battery cooling system 516independently provides cooling fluid to each battery module. The batterymanagement system 512 is configured to control the battery coolingsystem 516 to maintain the one or more battery modules 502 in a normaltemperature range.

The one or more electric drive units 514 provide propulsion to theelectric vehicle. When an electric vehicle is accelerated quickly, theone or more electric drive units 514 provide a large load on the one ormore battery modules 502. This can cause an increase in temperature inthe battery modules. The battery management system 512 can respond tothe large load by causing the battery cooling system 516 to provideincreased cooling to the battery modules 502. For example, the coolantflow rate can be increased and/or the coolant temperature can bedecreased to remove the heat generated by the large load.

The user interface 518 can be any suitable user interface. In someembodiments, the user interface comprises a display screen (e.g., aninstrument panel display). The display screen can be an LCD display, anOLED display, and LED display or any other type of display. In someembodiments, the user interface comprises a speaker. The user interfacecan operate under the control of the battery management system 512 topresent information (e.g., visual and/or audio information) to the user.

In accordance with the present disclosure, the battery management system512 may use one or more gas sensors to correlate gas concentration tobattery cell temperature. By monitoring the gas concentration, thebattery management system 512 is able to determine, as explained above,what temperature region the battery cells are operating within (e.g., asafe operating region, a cell overheating region, a cell ventilationregion, or a thermal runaway region). In some embodiments, batterymanagement circuitry is configured to receive a sensor signal from a gassensor, determine whether the sensor signal indicates the presence ofgas within a battery module (e.g., by comparing the sensor signal to oneor more thresholds as described above in connection with FIGS. 1, 3, and4), and take an action in response to determining that the sensor signalindicates the presence of gas. In some embodiments, the batterymanagement circuitry adjusts the threshold based on the usage of thebattery module. When the presence of gas indicates that a battery moduleis in a cell overheating condition, this predicts the onset of cellventilation. Such a determination, depending on the cause of the celloverheating, may provide sufficient time (e.g., several minutes or up to20 minute or more) to prevent ventilation from occurring.

The battery management circuitry may take one or more actions to preventventilation from occurring. For example, the battery managementcircuitry may perform one or more of the following actions: increasecooling (e.g., by instructing the battery cooling system to increasecooling); decreasing current flow in the battery module (e.g., bylimiting the maximum load that can be applied to the battery module);providing a warning to the user (e.g., using the user interface todisplay a warning or sound an alarm); and disconnecting the batterymodule (e.g., by activating a contactor coupled to an electrical outputof the battery module). In some embodiments, the battery managementcircuitry may progressively take actions if the gas concentrationcontinues to increase. For example, the battery management circuitry mayfirst increase cooling. If the gas concentration continues to increase,the battery management circuitry may additionally decrease the currentflow in the battery module. If the gas concentration continues toincrease, the battery management circuitry may display a warning to theuser. If the gas concentration continues to increase, the batterymanagement circuitry may disconnect the battery module to shut down thevehicle. In some embodiments, the battery management circuitry may takeone or more first actions when the battery cells are operating withinthe cell overheating region (e.g., to try to prevent cell ventilation)and may take one or more second actions when the battery cells areoperating within the cell ventilation region (e.g., to try to preventthermal runaway). The battery management circuitry may take one or morethird actions (e.g., disconnecting the battery) when the battery cellsare operating within the thermal runaway region.

It will be understood that the battery management circuitry may evaluatethe gas concentration of a single gas sensor or the concentration ofmultiple gas sensors, each configured to detect a different type of gas,to determine what temperature region the battery cells are operatingwithin. It will also be understood that the battery management circuitrymay receive one or more additional sensor signals (e.g., a temperaturesensor signal or a pressure sensor signal) to evaluate additionalinformation to determine the temperature of the battery cells. Forexample, if a battery cell is slowly overheating, the gas concentrationmay first begin to increase, then the temperature reading of atemperature sensor may begin to increase, and then the pressure readingfrom a pressure sensor may begin to increase after ventilation orthermal runaway (e.g., a large pressure increase may occur afterventilation and again after a thermal runaway). Accordingly, by usinginformation from one or more additional sensors, the battery managementcircuitry is able to more accurately determine the temperature of thebattery cells and more accurately predict the onset of cell ventilationor a thermal runaway. For example, if the gas concentration isincreasing at a slow rate and crosses a threshold, the batterymanagement circuitry may not determine that the battery cells areoperating in a cell overheating region unless a temperature reading alsoshows an increase in temperature. However, if there is a relatively fastincrease (e.g., a high rate of change) in gas concentration, the batterymanagement circuitry may determine that the battery cells are operatingin the cell overheating region regardless of whether a temperaturereading shows an increase in temperature. Accordingly, the batterymanagement circuitry can use both the gas concentration and the changein gas concentration to determine a battery module condition.

It will also be understood that the techniques of the present disclosurecan correlate the concentration of a detected gas (e.g., released froman adhesive) measured by a single gas sensor to the temperature of thatmaterial. By proxy, the techniques of the present disclosure also enablethe concentration to be correlated to battery cell temperature.Accordingly, battery cell temperature can be determined based on thepresence of gas in the battery module (e.g., when a material isconfigured to off-gas at a particular temperature) or concentration ofgas in the battery module (e.g., based on empirical data correlatingbattery cell temperature to gas concentration).

The techniques of the present disclosure provide various improvements tothe design and operation of battery modules. In a battery module, unlessevery single cell in the module has its own temperature sensormeasurement, there will always be incomplete temperature sensingcoverage. For battery modules with a large number of battery cells, itis impractical to provide each battery cell with its own temperaturesensor. When not every battery cell has its own temperature sensor,battery cell temperature measurements are inferred or modeled and it isdifficult or impossible to detect localized or single cell temperatureincreases that precede cell ventilation. The use of the gas sensor ofthe present disclosure overcomes these problems and provides an earlywarning of the onset of cell ventilation, thereby enabling actions to betaken to reduce the likelihood of cell ventilation and thermal runaway.

The foregoing is merely illustrative of the principles of thisdisclosure and various modifications may be made by those skilled in theart without departing from the scope of this disclosure. The abovedescribed embodiments are presented for purposes of illustration and notof limitation. The present disclosure also can take many forms otherthan those explicitly described herein. Accordingly, it is emphasizedthat this disclosure is not limited to the explicitly disclosed methods,systems, and apparatuses, but is intended to include variations to andmodifications thereof, which are within the spirit of the followingclaims.

What is claimed is:
 1. A system, comprising: a battery modulecomprising: a plurality of battery cells; a component thermally coupledto the plurality of battery cells, wherein the component is configuredto release a gas when a temperature of the component increases above anactivation temperature lower than a cell ventilation temperature range,wherein the cell ventilation temperature range causes at least onebattery cell of the plurality of battery cells to begin venting; and agas sensor configured to detect the presence of the gas within thebattery module; and battery management circuitry configured to: receivea sensor signal from the gas sensor; determine whether the sensor signalindicates the presence of the gas within the battery module; and inresponse to determining that the sensor signal indicates the presence ofthe gas, take an action.
 2. The system of claim 1, further comprising: abattery cooling system configured to provide cooling to the plurality ofbattery cells, wherein the action comprises using the battery coolingsystem to provide increased cooling to the plurality of battery cells.3. The system of claim 1, wherein the action comprises one of limiting amaximum load that can be applied to the battery module and disconnectingthe battery module from a load.
 4. The system of claim 1, furthercomprising: a user interface, wherein the action comprises using theuser interface to provide a warning.
 5. The system of claim 1, wherein:the component was doped with a chemical; when the temperature of thecomponent increases above the activation temperature, the componentbegins to off-gas the gas from the chemical.
 6. The system of claim 5,wherein the component comprises an adhesive used to secure the pluralityof battery cells in the battery module.
 7. The system of claim 1,wherein the gas sensor is a first gas sensor, the battery module furthercomprising: a second gas sensor configured to detect at least onechemical that is indicative of battery cell ventilation.
 8. The systemof claim 1, wherein the gas sensor is a first gas sensor, the batterymodule further comprising: a second gas sensor configured to detect atleast one chemical that is indicative of a battery cell thermal runawayevent.
 9. The system of claim 1, wherein the battery managementcircuitry is configured to determine whether the sensor signal indicatesthe presence of the gas within the battery module by: determiningwhether the sensor signal indicates that a concentration of the gas isgreater than a threshold.
 10. The system of claim 1, wherein the batterymanagement circuitry is configured to: determine a first battery modulecondition when the sensor signal indicates that a concentration of thegas is greater than a first threshold; and determine a second batterymodule condition when the sensor signal indicates that a concentrationof the gas is greater than a second threshold greater than the firstthreshold.
 11. The system of claim 1, further comprising: at least onetemperature sensor, wherein: the battery management circuitry isconfigured to: receive at least one temperature sensor signal from theat least one temperature sensor; and determine a battery modulecondition based on the sensor signal and the at least one temperaturesensor signal.
 12. A method, comprising: releasing a gas, from acomponent thermally coupled to a plurality of battery cells, when atemperature of the component increases above an activation temperaturelower than a cell ventilation temperature range, wherein the cellventilation temperature range causes at least one battery cell of theplurality of battery cells to begin venting; receiving a sensor signalfrom a gas sensor configured to detect the presence of the gas within abattery module, wherein the battery module comprises the plurality ofbattery cells; determining, using battery management circuitry, that thesensor signal indicates the presence of the gas within the batterymodule; and in response to determining that the sensor signal indicatesthe presence of the gas, taking an action.
 13. The method of claim 12,wherein taking the action comprises providing increased cooling to theplurality of battery cells using a battery cooling system.
 14. Themethod of claim 12, wherein taking the action comprises one of limitinga maximum load that can be applied to the battery module anddisconnecting the battery module from a load.
 15. The method of claim12, wherein taking the action comprises using a user interface toprovide a warning.
 16. The method of claim 12, further comprising:doping the component of the battery module with a chemical, wherein whenthe temperature of the component increases above the activationtemperature, the component begins to off-gas the gas from the chemical.17. The method of claim 16, wherein the component comprises an adhesive,the method further comprising: using the adhesive to secure theplurality of battery cells in the battery module.
 18. The method ofclaim 12, wherein the gas sensor is a first gas sensor, the methodfurther comprising: receiving a second sensor signal from a second gassensor configured to detect at least one chemical that is indicative ofbattery cell ventilation.
 19. The method of claim 12, wherein the gassensor is a first gas sensor, the method further comprising: receiving asecond sensor signal from a second gas sensor configured to detect atleast one chemical that is indicative of a battery cell thermal runawayevent.
 20. The method of claim 12, wherein determining whether thesensor signal indicates the presence of the gas within the batterymodule comprises determining whether the sensor signal indicates that aconcentration of the gas is greater than a threshold.
 21. The method ofclaim 12, wherein: determining whether the sensor signal indicates thepresence of the gas within the battery module comprises: determining afirst battery module condition when the sensor signal indicates that aconcentration of the gas is greater than a first threshold; anddetermining a second battery module condition when the sensor signalindicates that a concentration of the gas is greater than a secondthreshold greater than the first threshold; and taking the actioncomprises: taking a first action in response to determining the firstbattery module condition; and taking a second action in response todetermining the second battery module condition.
 22. The method of claim12, further comprising: receiving at least one temperature sensor signalfrom at least one temperature sensor; and determining a battery modulecondition based on the sensor signal and the at least one temperaturesensor signal.